1. Field of the Invention
The invention relates to a method of printing a multilayer structure using radiation curable ink. Furthermore, the invention relates to a printing system, in particular an ink jet printing system, for printing a multilayer structure using radiation curable ink.
2. Description of the Related Art
WO 2008/077850 A2 describes a 3D-inkjet printing method comprising the steps of: providing two or more fluids having a different composition to an inkjet printer; mixing the two or more fluids in a controlled amount; and jetting the mixture of the two or more fluids with the inkjet printer onto a support; at least partially curing the jetted mixture by actinic radiation or electron beam; and repeating the steps of mixing, jetting and curing in order to build a 3D-relief on the support. In one example, the composition of mixture made in the mixing step is changed at least once for the step of repeating the steps.
WO 03/029366 A1 describes a UV curable composition useful for three-dimensional inkjet printing comprising at least one UV curable urethane (meth)acrylate resin; at least one wax; at least one (meth)acrylate diluent; at least one photoinitiator; and at least one polymerization inhibitor; wherein the amount of wax is sufficient to phase change the UV curable composition after jetting.
US 2012/0282448 A1 describes a method for fabricating a three-dimensional object including depositing a composition containing a cationically curable compound, a cationic photoinitiator, a radically curable compound, a radical photoinitiator, and a gellant upon a surface to create a three-dimensional object; and curing the composition.
EP 1462266 A1 describes a method for forming a three-dimensional relief image on a support using an ink jet system, the relief image having a lamination image laminated on a first layer image that is a two-dimensional image.
Using radiation curable ink, in particular UV curable ink, multilayer structures may be printed that can reach a considerable height as compared to conventionally printed images that are basically flat, or, at least, the height of which is generally disregarded. By repeatedly printing a layer on top of a previously printed, cured layer, a multilayer structure may be built up having a defined height. For example, the height may be more than 0.1 mm, in particular more than of 0.2 mm, and e.g. up to 10 mm. The height, i.e. the thickness of the printed structures, adds an extension in a further dimension to the two dimensional image, and, accordingly, such prints are termed 2.5D prints. They are distinguished from 3D structures in particular in that the extension in the third dimension is limited to a thickness above a receiving material, i.e. there are no openings below a printed layer. Furthermore, the printed structure may comprise an image, e.g. a color image.
When printing a multilayer structure having a specific height using radiation curable ink, e.g. a multilayer structure that is a part of a 2.5D print, mechanical stress between the structure and a receiving material may arise when the ink shrinks during the curing of the ink. A problem of mechanical stress may be particularly pronounced in thick structures having e.g. a height of 0.5 to 10 mm. This may cause a detachment of the printed structure or, in case of a thin and/or flexible receiving material, a deformation may occur. Furthermore, mechanical stress between the printed structure and the receiving material may be caused by a thermal expansion coefficient difference between the ink and the receiving material. The mechanical stress accumulates along the lateral extension of the printed structure, so that the problem is particularly pronounced when printed structures have a large extension in one or two directions on the surface of the receiving material.
It is an object of the invention to provide a system and method that offer the possibility to alleviate the above mentioned problems.